MB-9834 Log how long certificate and private key generation takes.

Change-Id: Iaa289481651b4bba132ceb6e654c1f36f252a3ea
Reviewed-on: http://review.couchbase.org/31687
Tested-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>